The present invention relates to an auxiliary air control valve which is used for an engine so that air is supplied to the engine in the warm-up thereof while bypassing a throttle valve.
FIG. 3 shows a sectional view of a conventional auxiliary air control valve disclosed in the Japanese Patent Application (OPI) No. 5856/84 (the term "OPI" as used herein means an "unexamined published application"). Shown in FIG. 3 is an engine 1 which is supplied with intake air through an intake passage 2 provided with bypasses 4a and 4b disposed to by-pass a throttle valve 3. A valve casing 5 has an air inlet port 6 and an air outlet port 7, which are connected to the by-passes 4a and 4b. The valve casing 5 also has a valve seat 9 provided on an internal air passage, which extends to connect the air inlet port 6 and the air outlet port 7 to each other. The valve seat 9 has a valve port 10 of prescribed minimum diameter. A valve element 20 is disposed in the face of the valve seat 9 to control the cross-sectional area of the internal air passage, and has a tapered tip portion 22. A spring 26 urges the valve element 20 in such a direction as to open the auxiliary air control valve. An actuator 14 functions to move the valve element 20 against the force of the spring 26, and contains thermowax which expands or contracts depending on the temperature of cooling water 15 from the engine 1. The actuator 14 comprises an output rod 23, which is moved in or out by the expansion or contraction of the thermowax, and a cylinder 21 for guiding the output rod.
When the temperature of the cooling water 15 for the engine 1 rises in the warm-up or the like thereof, the actuator 14 responds to the rise in the temperature so as to move the valve element 20 toward the valve seat 9 to decrease the cross-sectional area of the internal air passage to reduce the supplied quantity of auxiliary air.
When the temperature of the cooling water 15 has reached a prescribed level, the tapered tip portion 22 of the valve element 20 is tightly placed in the valve port 10 of the valve seat 9 to render the cross-sectional area of the internal air passage zero to make the supplied quantity of the auxiliary air zero. When the temperature of the cooling water 15 has exceeded the prescribed level the thermowax in the actuator 14 expands further to protrude the output rod 23. Since the output rod 23 and the valve element 20 are elastically coupled to each other, the output rod is allowed to be moved forth even if the valve element is put in contact with the valve seat 9 and therefore cannot be moved forth. A cylindrical member 24 is attached to the output rod 23 and slidably fitted on the cylinder 21. A spring 25 is provided between the cylindrical member 24 and the valve element 20 and urges the valve element in such a direction as to close the auxiliary air control valve. An engaging member 27 is provided between the valve element 20 and the output rod 23 to prevent the valve element from being uncoupled from the output rod by the spring 25.
Although the conventional auxiliary air control valve functions so as to prevent undesirable stress from being caused in the valve seat 9 through the action of the valve element 20 by the output rod 23 being protruded even after the temperature of the cooling water 15 has reached the prescribed level, the valve has problems in that the constitution of the valve is complicated, a large number of component parts are needed for the valve and the cost of production of the the valve is high.